In a liquid chromatography ultraviolet detector, resolution can directly impact the capabilities of the instrument to uniquely identify substances. Resolution is the measure, in nanometers, of how far apart in wavelength two light signals are so that the detector can accurately be distinguished one from the other. Many variables can impact resolution, however. For example, two factors that set the maximum theoretical resolution are slit width and linear dispersion of the diffraction grating. Thevenon, J. M. L. and A., A Tutorial on Spectroscopy, 2003.
Other factors that can impact the ultraviolet detector include optical bandwidth, wavelength range and dynamic capability. The optical bandwidth of a detector is the breadth of the minimum spectra that a machine is capable of detecting. It can be equal to, or more often, greater than the resolution of the detector. For example, if an instrument has a resolution of 1 nm and an optical bandwidth of 5 nm, the detector can detect absorption between 250 nm and 255 nm or between 251 nm and 256 nm. Wavelength range is the portion of the electromagnetic spectrum in which a detector can operate and is set either by the spectral distribution of the light source or the design of the optical system. Methods for absorption spectroscopy are often designed around a specific wavelength or set of wavelengths. Therefore, a range of wavelengths over which a detector can operate often determines its useful application.
Likewise, the noise arising from the quantized nature of light, called the shot noise, often dominates the signal to noise ratio (“SNR”) in UV detectors. Yariv, A., Introduction to Optical Electronics Holt, Rinehart & Winston Series in Electrical Engineering, Electronics, and Systems, 2nd ed. Holt, Rinehart and Winston, 1976. Often liquid chromatography is used as a method to determine not what a sample is composed of, but rather how much of a given substance is present in the sample. Yet, nearly every component of the detector and its environment has the potential to add some amount of noise to the signal. The addition of a reference can reduce or eliminate many forms of noise.
Furthermore, dynamic capabilities of a detector, or the set of features which can be used while samples are running, such as reference-based noise canceling, baseline adjustments, on-the-fly self-calibration, timesharing among multiple wavelengths, and actively modulating the source or entrance slit, often are lacking in the device. Dynamic features add flexibility and robustness to a detector, and provide a device for backwards and forwards compatibility.
A need exists for the liquid chromatography detector that is efficient, compact having low heat generation and dynamic in nature, having both backwards and forwards compatibility.